EP0275819B1 - Labyrinth-type filter for the dielectric fluid of electro-discharge machines - Google Patents

Description

The invention relates to a labyrinth filter for the spherical metal particles in the dielectric of eroding systems, and to a filter system with at least one such labyrinth filter.

As is known, the dielectric of erosion systems has to be continuously freed of impurities in the form of spherical metal particles of the order of magnitude of 1 to 20 μ, which are removed during the erosion process. Known filters for eroding systems are based on the principle of forced filtration, with the particles remaining in and in front of openings that are smaller than their diameter. Such filters can be found, for example, in US Pat. No. 3,469,057 and in the publication "Werkstatttechnik", January 1970, pp. 41-42. A bed of metal particles builds up relatively quickly, which eventually clogs the filter. Known filters of this type, such as kieselguhr filters or cartridges with fabric-like filters, therefore have a relatively short service life and must be replaced or serviced periodically. The periodic replacement or regeneration of the filters leads to a large amount of non-reusable waste, is cost-intensive and requires periodic manual interventions to change the filters, which is a fully automatic process Long-term operation, eg over the weekend, is excluded without monitoring.

Other devices and methods, mainly based on sedimentation and the use of magnets, for separating metal particles from the dielectric of erosion systems have also become known, e.g. described in EP-A 0 098 711, which, however, is very complex and has not proven itself in practice.

On the other hand, of course, sand filters have become known as such in many forms for removing dirt from liquids. For this purpose, reference can be made to the publications FR-A-2 364 053, US-A 3 842 001, and FR-A-1 532 544. Without exception, these filters are characterized by a pass-through height that corresponds approximately to the filter diameter. It has been shown that such conventional sand filters do not retain the microscopic, spherical metal particles that arise during the spark erosion process. Therefore, such filters have not been used to clean the dielectric of EDM systems.

It is therefore the task of creating a filter for the small spherical metal particles from EDM systems, which has a longer service life, is easy to clean and reusable, and enables fully automatic long-term operation without manual intervention.

It has surprisingly been found that the above-mentioned object can be achieved by means of a labyrinth filter which is constructed according to claim 1.

In contrast to the aforementioned forced filtration, the labyrinth filter is based on the effect that the microscopic spherical metal particles are caught in larger gaps in the flow-related rest and vacuum zones.

In contrast to conventionally used filters, in which a fine-meshed grid prevents the particles from flowing along and thus forced filtering takes place, in the labyrinth filter the large number of randomly existing quiet zones, which are present in every regularly flowing labyrinth, are used for the accidental deposition of the metal particles .

Such a labyrinth is expediently constructed from inexpensive granular or spherical materials which have no connections with metal particles come in. The surface of the grain is preferably as fine as possible so that as little flow resistance as possible is opposed to the liquid flowing through. The shape and size of the grain should be different in order to locally build up the greatest possible number of different pressures and flow velocities on the surface half of the grain facing the outlet side.

For the reasons mentioned, the labyrinth filter has its effect on the microscopic spherical metal particles only from a certain flow rate of the dielectric through the filter, the filtering effect mainly not resulting from the construction of a bed of metal particles retained in the lattice, as is the case with the forced filtration of the Case, but by filling the above-mentioned quiet zones with metal particles over the entire filter height. In this way, the labyrinth filter is used over its entire height. It requires a minimal backwash flow for regeneration. If the grains of the labyrinth are brought out of their position even slightly, the deposited particles are immediately free again. The labyrinth can therefore be flushed back either in pulses or with strongly changing pressures in order to prevent a filter effect in the opposite sense.

As already mentioned, the removed particles in eroding processes are not suitable for sedimentation processes immediately after they are formed. They remain in suspension for a very long time, so that the duration of the weaning process is too long for practice.

Surprisingly, however, it has been shown that the metal particles in the labyrinth filter form conglomerates which can be removed from the rinsing liquid within a useful period of time. The liquid that is sufficient for practical purposes above the deposited dirt layer can therefore be returned to the backwash tank before the next backwash. This makes a closed backwash cycle for regeneration possible.

In order to have the backwashing and filtering processes run automatically, a large number of controlled valves would be necessary which, on the one hand, would jeopardize operational safety due to the failure and, on the other hand, would necessitate a complicated and costly construction of the system. There is a particular risk that the valves will become clogged with time by the metal particles in the dielectric, in particular if they adhere to magnetized valve parts. A central valve according to claim 9 is therefore preferably used. With three positions of the central valve, all necessary connections can be created.

• Fig. 1 eine schematische Schnittdarstellung eines Labyrinthfilters;
• Fig. 2 eine schematische Darstellung der gesamten Filteranlage mit zwei Filtereinheiten, Zentralventil und Absetzteil für die Rückspülflüssigkeit
• Fig. 3 eine schematische Darstellung des Zentralventils;
• Fig. 4 eine Schnittdarstellung der Steuerplatte und der Dichtplatten des Zentralventils in einer ersten Ausführung;
• Fig. 5 eine Aufsichts- und Schnittdarstellung einer zweiten Ausführung einer Dichtplatte des Zentralventils;
• Fig. 6 eine schematische Ansicht der Verbindungsleitungen der Anlage;
• Fig. 7 eine Explosionsansicht der einzelnen Ventilplatten des Zentralventils in seinen drei Betriebszuständen.
• Fig. 8 eine Darstellung eines Rückhaltelementes;
• Fig. 9 eine zweite Ausführung eines Rückhalteelementes.

In Fig. 1 ist zunächst eine Filtersäule des Labyrinthfilters zusammen mit Kühlaggregaten dargestellt.An exemplary embodiment of the invention is described in more detail below. The attached figures show:

• Fig. 1 is a schematic sectional view of a labyrinth filter;
• Fig. 2 is a schematic representation of the entire filter system with two filter units, central valve and settling part for the backwashing liquid
• 3 shows a schematic illustration of the central valve;
• Figure 4 is a sectional view of the control plate and the sealing plates of the central valve in a first embodiment.
• Figure 5 is a top and sectional view of a second embodiment of a sealing plate of the central valve.
• Fig. 6 is a schematic view of the connection lines of the system;
• Fig. 7 is an exploded view of the individual valve plates of the central valve in its three operating states.
• 8 is an illustration of a retaining element;
• Fig. 9 shows a second embodiment of a retaining element.

In Fig. 1, a filter column of the labyrinth filter is shown together with cooling units.

As already mentioned, it can be assumed that it is not primarily the entry surface 30 that can be used to switch back the metal particles that occur, but that, due to the spherical shape of the metal particles, the flow-related “quiet zones” behind the filter grains enable the metal particles to be retained. Therefore, the filter is built with a large passage height 31 in relation to the entry surface. Since the flow resistance is relatively low compared to other filters, the available room height limits the overall height.

As can be seen in particular from FIG. 6, the overall height can be reduced by connecting two filter units A and B in series. Each of these units is essentially designed according to FIG. 1. The two units A, B can be provided with a common cooling device, as shown in FIG. 1. In this figure, only one of the units A is visible, while one has to imagine the other one covered by this unit.

The filter units each have a pressure container 21, in which the filter grains K are filled in loosely.

The pressure vessels are not completely filled. The space remaining above serves to allow the volume of the filling to expand during backwashing, so that the individual filter grains can separate from each other and set themselves free to move in the backwashing liquid.

An upper collecting chamber 22 and a lower collecting chamber 23, on which the inlet connection EA and the outlet connection AA are arranged, are attached to the base body of the pressure vessel with screwed flanges. The dielectric to be filtered is fed in through the inlet connection EA at the top, which is conveyed out of the erosion container by means of a filter pump FP (cf. FIG. 2.6). The performance of the filter pump, the inlet surface and the flow height of the labyrinth filter are matched to one another in such a way that the flow rate of the dielectric through the filter is above a limit value of approximately 2, preferably 3 meters / min. lies. At Flow speeds below 2 meters / min. the resulting negative pressure zones or quiet zones, in which the microscopic metal particles are trapped, are no longer available in the desired strength, and the filter effect is no longer guaranteed.

In the present exemplary embodiment, the tube diameter is 211 mm, which corresponds to an entry surface of 3.5 dm2. The labyrinth height per filter unit is approx. 1400 mm, i.e. a total of approx. 2800 mm in series operation. The filter grains made of quartz sand have a grain size between 0.3 and 0.7 mm. The free flow cross section is about 7% of the inlet surface mentioned. In operation, the filter pump has a volume of 26 to 32 liters / min. promoted. The flow rate in the labyrinth is at an average value of 28 liters / min. in normal operation about 11 meters / min. It is therefore much higher than with conventional sand filters.

With these values, a flow velocity of the dielectric through the labyrinth is achieved, which in each case on the side of the filter grains facing away from the inflow side, flow-related negative pressure zones can arise, in which the microscopic metal particles accumulate.

The process heat generated during erosion and the heating of the dielectric caused by the pumps require cooling of the dielectric. This can advantageously be combined with the filtration, as shown in FIG. 1. The cooling is carried out with a fan 33 and an upwardly open cooling water tank 38, which holds the filter in the lower third encloses, supported by non-woven fabric 39, which tightly encloses the pressure vessel of each filter unit as far as possible and distributes the water over as large a surface as possible for evaporation, as well as with cooling fins 31, which are attached to the outside of the pressure vessel in the upper third. The enrichment of the air with moisture caused by the erosion process and the cooling requires an air dehumidification system 34, which can also be integrated into the filter system. The undesirable air humidity is thus reduced and the water obtained is returned to the circuit via line 40. Line 40 is a connection to the dielectric tank of the eroding system. The dehumidification is achieved with a cooled body 34 in the air flow of the fan 33, on which the air humidity condenses. Another design feature of the filter are the retaining elements 25 (FIG. 8), which are also installed in the inlet chamber and prevent the grains from floating out during the backwashing process. The filter grains K would be flushed out without retaining elements in the inlet chamber during backwashing. The retaining elements consist of coil springs 50, which are mounted on a core 52 with through channels. The mutual distances between the turns are smaller than the size of the grains. FIG. 9 shows a second possible embodiment of a retaining element 25 with individual spring elements 51 clamped onto the core.

In order not to have to interrupt the operation of the system for the periodic cleaning of the filters by backwashing, each of the filter units A, B can be separated be backwashed while the other maintains filter operation. In normal operation, the filter units A, B are operated in series. The interconnection of the filter units via a central valve 1, which produces all connections in three operating positions, is shown in more detail in FIG. 6.

In a first position, the central valve 1 ensures that the dielectric flows through the first filter unit A in normal operation and then through the second filter unit B, which is connected in series, from top to bottom. The clarified dielectric flowing out of the outlet AB of the second unit is then fed to a clean tank ST, from where it is in turn continuously conveyed to the processing machine. This creates a closed circuit of dielectric, which in the present system is not interrupted even when the filter units are cleaned. To periodically clean the filter units, one of the units is backwashed while the other remains in the circuit. The backwashing is also carried out by means of a dielectric which is fed from a backwashing tank E to the respective filter unit by a backwashing pump RP which is switched on and off in intervals. flows with strongly changing pressures from bottom to top. As a result, the grains forming the filter labyrinth are set in free movement in the backwashing liquid and the aforementioned quiet zones for the metal particles are eliminated, so that they are flushed out with the backwashing liquid.

The backwash liquid loaded with the filter residues is in each case a settling tank C. supplied, on the bottom 46 of which the metal particles settle, as will be explained in more detail. The backwash liquid lying above is then fed back to the backwash tank E via a valve V1, while the sediment of metal particles reaches a drying tank D via a valve V2. The central valve 1 creates all the connections necessary for these functions in the area of the filter units A and B, as can be seen in FIG. 6.

The central valve 1, as can be seen from FIG. 7, is constructed as a plate package from a plurality of perforated plates 6 to 14. One of the plates is designed as a control plate 10 and can be moved between three positions, each position corresponding to one of the previously mentioned operating states. These three positions are shown side by side in FIG. 7. The plate package consists of a connection plate 14 from top to bottom, which carries the 5 connections C, FP, EB, ST and RP. Below this is a first connecting channel plate 13, which is followed by a sealing plate 12 with a hole pattern. A corresponding sealing plate 11 is arranged on the other side of the control unit 10 lying in between. After the lower sealing plate 11 is followed by a second connection channel plate 9, a locking plate 8, a third connection channel plate 7 and the lower connection plate 6, with 3 connections EA, AA and AB. The connecting duct plates are always surrounded by perforated plates, which form defined passages of the diameter of the connecting lines.

The working position is shown on the left in FIG. 7, in which the two filter units A, B are operated in series. The valve will like visible, flowed in a straight line. Dielectric enters the valve from the filter pump at connection FP and exits again at connection EA, which is connected to the inlet of filter unit A. The dielectric then passes through this filter unit, the outlet of which is connected to connection AA of the valve package. The dielectric reaches the EB terminal from the AA terminal and is fed from there to the inlet of the second filter unit B. From their outlet, the dielectric reaches the clean tank via the AB and ST connections of the valve. The two backwash positions are shown in the middle and the right picture of FIG. 7, the middle picture showing the backwashing of the filter unit A, the right picture that of the filter unit B, as the corresponding designations in comparison with FIG. 6 immediately reveal and therefore here is not explained in detail.

In the state of operation, the seal between the different valve channels is guaranteed. On the sealing plates 11 and 12, in which the seal must be ensured despite its displaceability, as shown in FIG. 4, each hole on the sides facing the control plate 10 is surrounded by a sealing ring 41 which is connected to the respective bore in the control plate 10 or cooperates with the uninterrupted surface of the control plate 10. The sealing rings 41 are made of plastic and adapt to smaller bumps on the control plate 10. They are pressed against the sealing plates by elastic rings 42.

5 shows a modification of the sealing plate structure. The sealing plates 11, 12 have instead of individual sealing rings a common sealing washer 43 for all holes, which is also pressed by means of elastic rings 42 against the control plate 10 and forms a sliding seal.

In order to achieve the tightness of the valve during operation, but at the same time to ensure small displacement forces for the control plate 10 and to avoid the wear of the sealing rings 41 and the sealing disk 43, the plate pack is held together by a clamping device 45, which allows the plates to be fixed with a certain amount Force squeeze. This clamping device is shown in more detail in FIG. 3, in which the plate pack is shown schematically. The plate pack is held together by the plates 6 and 15 by means of screws 17, on which the plates are slidably mounted. Springs 29 give an always existing pre-tension, which ensures the seal to the outside and between the individual channels in the valve.

The central valve 1 is composed of correspondingly perforated low-pressure polyethylene plates, which are very simple and inexpensive to manufacture. The control plate 10 can be brought into its three positions with a motor drive 2 via an eccentric 3 (FIG. 3).
This drive is connected to a central control, which allows the entire operation of the system to run automatically.

The explained two-stage backwashing process is triggered when the first filter unit A is so dirty that pressure builds up in its inlet chamber then triggers the cleaning program already explained. The drive of the control plate 10, as well as the valves V1 and 3 and the corresponding pumps are actuated in a programmed sequence by the central control, the filter pump FP and the backwash pump RP being switched off during the displacement of the control plate 10.

The central valve described has the advantage that there are only three defined switching states. This means that if a single valve fails, the liquid is misdirected. This significantly simplifies control. The number and length of the connecting hoses can be significantly reduced. In the working state, the valve is flowed through without deflections, which prevents dirt accumulation.

Through the periodic backwashing mentioned, the microscopic metal particles with the backwashing liquid are shipped into the settling tank C (see FIGS. 2 and 6). In the labyrinth filter, these particles have combined to form conglomerates, which settle relatively quickly in the settling tank. In the case of metal particles that come directly from the eroding machine, this is not the case by forming floating particles that cannot be deposited even after a very long time. The labyrinth filter according to the invention thus has the effect of combining the metal particles into stable conglomerates, which accumulate on the floor in the settling tank after a relatively short time. As already mentioned, the backwash liquid above it can be fed to the backwash tank E after clarification and stands for the next backwash is available. The backwash circuit thus also forms a closed circuit, from which the conglomerated metal particles removed during erosion are separated in the settling tank C and the drying tank D. In the drying tank D, the sediment from the sedimentation tank is deposited on a filter mat, through which the residual liquid can also drain into the backwash tank. The erosion residues dried on the filter mat solidify like bricks and can be used for scrap metal recycling.

Finally, in Fig. 2 the above system is shown in a compact design as it is used in companies. Several erosion machines can be connected to this system, the filter pump FP conveying the contaminated dielectric from the erosion containers into the filter system and from there into a clean tank ST (shown schematically), from which the cleaned dielectric is in turn fed to the erosion containers.

Claims (12)

1. A labyrinth filter for removing spherical particles generated by the erosion process from the dielectric of a spark erosion apparatus, characterized in that the filter comprises at least one filter column (A, B) through which flow occurs longitudinally, containing loosely filled grains (K) forming a labyrinth, and a feed pump connected to the inlet end of the filter column wherein the flow height of the filter column is about six times the column diameter related to a circular cross-section and wherein the velocity of flow of the dielectric through the labyrinth generated by the feed pump is at least 2 meters per minute.
2. A labyrinth filter in accordance with any of the preceding claims characterized in that the velocity of flow of the dielectric is about 11 meters per minute.
3. A labyrinth filter in accordance with any of the preceding claims, characterized in that filter grains (K), preferably quartz sand, measuring between 0.3 and 0.7 mm are used.
4. A labyrinth filter in accordance with any of the preceding claims, characterized in that the filter column (A, B) has a substantially constant diameter (30) over the entire flow height (31).
5. A labyrinth filter in accordance with any of the preceding claims, characterized in that the cross section of a filter column (A, B) is about 210 mm and its height measures about 1,400 mm.
6. A labyrinth filter apparatus comprising a labyrinth filter in accordance with any of the preceding claims, characterized in that a closed backwash circuit (E, RP, C) is provided comprising a deposit tank (C) for the backwash liquid, from which the backwash liquid can be supplied to a filter column (A, B) again.
7. A labyrinth filter apparatus in accordance with Claim 6, characterized in that at least two filter columns (A, B) are provided, and are connected via valves (1) to a closed filtration circuit in such a way that the columns can be operated either in series or separately, wherein each filter column (A, B) can be connected separately to the backwash circuit, while the other remains available for normal operation.
8. A labyrinth filter apparatus in accordance with Claim 7, characterized in that each of the filter columns (A, B) has a pressure tank (21), these tanks being arranged side by side and being provided with cooling means (38 - 43) to cool the pressure tanks at their outer surface.
9. A labyrinth filter apparatus in accordance with Claim 8, characterized in that the pressure tanks are provided with a jacket (36) through which a stream of cool air is directed over the outer surface of the pressure tanks.
10. A labyrinth filter apparatus in accordance with Claim 9, characterized in that the pressure tanks are partially surrounded with water and are cooled by the evaporation thereof, wherein the cooling air or the room air passes along a condenser (34) to recover the evaporated water from the air.
11. A labyrinth filter apparatus in accordance with any of the preceding claims 6 to 10, with at least two labyrinth filters which can be backwashed individually, characterized in that there is provided a central valve (1) having a stack (1) of perforated plates, one of which is provided to serve as a control plate (10) which can be moved between at least three positions, such that in the first position, all connections for filter operation with both filter columns (A, B) connected in series are established within the valve, and such that in each of the other two positions, all connections are established for backwashing one of the filter columns while leaving the other column in normal operation.
12. A labyrinth filter apparatus in accordance with any of the preceding claims 6 to 11, characterized in that a tank unit (C, D, E) connected to the backwash circuit is provided, consisting of at least said deposit tank and a backwash tank (E) connected to the deposit tank (C) and containing the liquid used for backwashing.

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